Chapter 12: The Auditory and Vestibular Pathways and Approach to Hearing Loss and Dizziness/Vertigo: Cranial nerve 8

Cranial nerve 8 (CN 8) contains two components: auditory (cochlear) and vestibular. Both begin in the inner ear and travel to the brainstem: the auditory component projects to the cochlear nuclei (at the pontomedullary junction) and the vestibular component projects to the vestibular nuclei (in the medulla).

Auditory information travels from the inner ear through the auditory (cochlear) portion of CN 8 to arrive at the cochlear nuclei at the pontomedullary junction (Fig. 12–1). The cochlear nuclei project to the inferior colliculi of the lower midbrain via the lateral lemniscus, and also project to the superior olives. Each inferior colliculus projects to the ipsilateral medial geniculate nucleus (MGN) of the thalamus, and each MGN projects to the ipsilateral auditory cortex in the superior temporal gyrus (Heschel’s gyrus).

Auditory information crosses to become bilateral early in its connections within the brainstem, so unilateral hearing loss can only occur due to pathology of the inner ear or CN 8 (or rarely the entry zone of CN 8 or cochlear nuclei at the pontomedullary junction). Central lesions (in the brainstem or temporal lobe) only rarely cause deafness, and must be extensive and bilateral to do so. Therefore, central etiologies of deafness are usually associated with other signs due to involvement of neighboring structures. Left temporal lobe lesions can lead to deficits in word processing (pure word deafness) and right temporal lobe lesions can cause deficits in music processing (amusia).

Hearing loss due to a peripheral lesion is called conductive hearing loss if it caused by problems in the outer or middle ear, and called sensorineural hearing loss if it is due to problems in the cochlea or auditory component of CN 8. Both conductive and sensorineural etiologies of hearing loss may be acquired or may have a congenital/genetic basis. Acquired causes of hearing loss are listed below.

Acquired causes of conductive hearing loss include:

• Outer ear: cerumen impaction

• Middle ear: infection (otitis media), otosclerosis

Acquired causes of sensorineural hearing loss include:

• Unilateral

  • Internal auditory artery infarct (the internal auditory artery [also called the labyrinthine artery] is usually a branch of the anterior inferior cerebellar artery [AICA])

  • Sudden sensorineural hearing loss (often idiopathic; may respond to steroids)

  • Ménière’s disease (see “Ménière’s Disease” below)

  • Vestibular schwannoma (also called acoustic neuroma; see “Vestibular Schwannoma” in Ch. 24)

• Bilateral

  • Aging (presbyacusis)

  • Ototoxic medications (e.g., aminoglycosides)

  • Sequela of meningitis (especially in children)

  • Neurofibromatosis type II with bilateral vestibular schwannomas (see “Neurocutaneous Syndromes” in Ch. 24)

  • Susac’s syndrome (a syndrome causing branch retinal artery occlusion, sensorineural hearing loss, and encephalopathy; see “Susac Syndrome” in Ch. 19)

  • Superficial siderosis (which causes hearing loss accompanied by cerebellar dysfunction and/or upper motor neuron signs; see “Superficial Siderosis” in Ch. 19)

  • Mitochondrial disorders (see “Mitochondrial Diseases” in Ch. 31)

Sudden-onset unilateral hearing loss can be caused by infarction of the inner ear structures due to ischemia in the territory of the internal auditory artery (also called the labyrinthine artery), which is usually a branch of the AICA. This diagnosis should be strongly considered in patients whose acute-onset unilateral hearing loss is accompanied by vertigo or other brainstem or cerebellar symptoms/signs. If hearing loss is episodic with a sense of ear fullness and vertigo, Ménière’s disease should be considered.

Distinguishing Conductive Hearing Loss From Sensorineural Hearing Loss

The function of the eardrum and middle ear bones is to amplify sound waves for transmission into neural impulses. In conductive hearing loss, CN 8 works properly, but sound is not able to be transmitted to it by the outer/middle ear. In sensorineural hearing loss, the pathway for auditory conduction is not functioning properly. The Weber and Rinne tests can help to distinguish between conductive and sensorineural hearing loss (Table 12–1).

Weber’s Test

In Weber’s test, a vibrating tuning fork is placed on the top of the patient’s head. Normally, the pitch should be heard equally in both ears. If the pitch is louder on one side, this means that either the opposite (softer) side is affected by sensorineural hearing loss or the ipsilateral (louder) side is affected by conductive hearing loss (outer/middle ear blockage masks outside noise, making conduction by way of the skull louder in that ear).

Rinne’s Test

In Rinne’s test, a vibrating tuning fork is placed on the patient’s mastoid and then next to the ear, and the patient is asked which is louder. Normally, the sound next to the ear should be louder because it takes advantage of the amplifier function of the middle ear bones. In conductive hearing loss, the middle ear bones are not working normally (e.g., otosclerosis, otitis media), or sound cannot adequately access the middle ear (e.g., cerumen impaction, otitis externa). Therefore, the tuning fork will sound softer next to the ear (since the amplifying mechanism of the middle ear is not functioning), but louder on the mastoid because it uses skull vibration to arrive directly at CN 8, taking a “detour” around the problem in the outer or middle ear. In sensorineural hearing loss, the tuning fork will be heard as diminished both on the mastoid and next to the ear since the final pathway (inner ear/CN 8) is not functioning. Air conduction is still usually louder than bone conduction in sensorineural hearing loss, as is the case normally.

The inner ear vestibular structures (saccule, utricle, and semicircular canals) detect movements of the head (Fig. 12–2). This information is transmitted by the vestibular portion of each CN 8 to the vestibular nuclei in the dorsolateral medulla, which then communicate with the cranial nerve nuclei for eye movements (CNs 3, 4, 6) via the medial longitudinal fasciculus (MLF). Vestibular information is also communicated to the vestibulocerebellum (the flocculus/nodulus of the cerebellum) via the inferior cerebellar peduncles (see Ch. 8). This coordination of eye movements with head movements allows for the vestibulo-ocular reflex.

The Vestibulo-Ocular Reflex (VOR)

When attempting to fixate gaze on a point while moving the head, the eyes must move in the opposite direction from the head (Fig. 12–3). For example, if you ask a patient to continue looking at your nose while turning the head to the right, the patient’s eyes will have to move to the patient’s left to maintain fixation. This vestibulo-ocular reflex (VOR) is accomplished by communication between the vestibular nuclei and the abducens nucleus on the left so as to coordinate left eye abduction (via CN 6) and right eye adduction (via MLF to CN 3).

The brain determines which way the head is turning by comparing information from the left and right vestibular systems. The side to which the head turns stimulates greater vestibular system excitation on that side, and this is communicated to the ocular motor nuclei by way of the MLF to turn the eyes to the opposite side. Turning the head toward the left causes the left vestibular system to become more activated than the right side, and this activation pattern is communicated through the MLF to the right abducens nucleus to send the eyes to the right (via the right CN 6 and left CN 3). Turning the head toward the right causes the right vestibular system to become more excited than the left side, and this excitement pattern is communicated through the MLF to the left abducens nucleus to send the eyes to the left (via the left CN 6 and right CN 3).

The VOR can be suppressed when needed. For example, if you want to turn both your head and your eyes to the left to look at something on the left side, you would not want your eyes being dragged to the right against your will as you try to look left. Although the decision to suppress the VOR likely comes from the hemispheres, suppression of the VOR is mediated by the vestibular portion of the cerebellum (flocculus and nodulus). The ability to suppress the VOR can be tested by having the patient sit in a swivel chair with the thumb held out at arms’ length, and then rotating the chair from side to side while the patient maintains fixation on the thumb. If the VOR cannot be suppressed, the eyes will move in the direction opposite chair/head turning rather than following the thumb. Failure to suppress the VOR can be seen in neurodegenerative disorders such as progressive supranuclear palsy (see “Progressive Supranuclear Palsy” in Ch. 23).

Oculocephalic Reflex

The oculocephalic reflex can be used to assess the VORs in a comatose patient to determine the integrity of brainstem pathways (although this should not be attempted if the cervical spine is injured). To test the oculocephalic reflex, the head is turned passively to look for the presence of conjugate eye movements in the opposite direction. Although the term “doll’s eyes” is often used for this test, it can be unclear whether “having doll’s eyes” means having an intact oculocephalic reflex or an abnormal one, so it is more precise to state whether the oculocephalic reflex is present or absent in each direction. Presence of oculocephalic reflexes in a comatose patient indicates that the brainstem pathways are intact, suggesting that the comatose state is due to pathology affecting the hemispheres. Oculocephalic reflexes may be impaired with brainstem pathology, but can also be diminished or absent with sedating medications, complicating assessment in comatose patients who are sedated.

Cold Caloric Testing

If a patient has neck trauma prohibiting oculocephalic reflexes from being safely tested by passive head turning, cold caloric testing can be pursued (as long as the tympanic membrane is intact). In this test, cold water is placed into one ear. Cold water “turns off” the vestibular apparatus. If one side is turned off, the other side’s normal baseline activity is “greater than off,” so the brain thinks the head is moving toward the not-cold side. This causes the eyes to move away from the not-cold side and toward the cold side.

For example, cold water in the left ear causes the left ear to be “off,” so the brain detects more activity from the right vestibular system compared to the “off” left ear. This simulates the head turning toward the right, and so the eyes move to the left (if the VOR pathway is intact). If the frontal lobes are intact, there will be nystagmus with the fast phase in the direction opposite the slow phase (i.e., the fast phase of the nystagmus is away from the cold side).

Cold caloric testing assesses both brainstem and hemispheric function. If both the brainstem and hemispheres are functioning, there will be both a slow phase toward the cold water side and nystagmus with fast phase away from the cold water side. If the brainstem is functioning but there is hemispheric dysfunction, there will only be a slow phase (toward the cold water side) and no fast phase. If there is no slow phase at all, this suggests that there is either disruption of brainstem vestibulo-ocular pathways or that the patient has taken or received sedating medications.

Nystagmus

Nystagmus is abnormal spontaneous rhythmic movement of the eyes. The type of nystagmus most commonly seen has a slow-phase in one direction and a fast phase in the opposite direction (jerk nystagmus). When nystagmus is present, the goal is to determine if the cause is peripheral (inner ear or CN 8) or central (brainstem/cerebellum).

Several types of nystagmus occur exclusively with central pathology (i.e., lesions of brainstem/cerebellum or drugs affecting them):

• Gaze-evoked, direction-changing nystagmus: The fast phase is in the direction of gaze in all eye positions (i.e., fast phase is toward the left when the patient looks left and toward the right when the patient looks right). This is called direction-changing nystagmus because the direction of the fast phase changes depending on the direction of gaze (i.e., right-beating when looking right, left-beating when looking left; see “Direction-Changing Nystagmus Due to Central Lesions” below).

• Pure vertical nystagmus (i.e., down-beating or up-beating nystagmus with no torsional component).

• Pure torsional nystagmus (i.e., with no horizontal or vertical component).

• Pendular nystagmus: In contrast to the more common jerk nystagmus, pendular nystagmus consists of symmetrically oscillating eye movements rather than movements with alternating slow and fast phases.

• The various more “exotic” and rare types of nystagmus, such as periodic alternating, see-saw, rebound, Brun’s.

Other useful localizing principles for nystagmus include:

• Nystagmus of peripheral origin can be suppressed by fixation, whereas nystagmus of central origin cannot. This is because when nystagmus is peripheral in origin, central mechanisms controlling fixation can overcome it.

• Nystagmus of central origin can be associated with additional brainstem and/or cerebellar signs. Nystagmus of peripheral origin may have accompanying hearing loss, but no other neurologic signs should be present. Both central and peripheral causes of nystagmus can be associated with nausea, dizziness, and imbalance.

Causes of nystagmus of central origin include:

• Stroke, demyelinating lesion, or tumor in the lower brainstem or cerebellum

• Medications (e.g., antiepileptics and lithium)

• Toxins (e.g., alcohol)

• Paraneoplastic cerebellar degeneration (see “Paraneoplastic Syndromes of the Nervous System” in Ch. 24)

• Genetic cerebellar degenerative diseases (e.g., spinocerebellar ataxia; see “Inherited Causes of Ataxia” in Ch. 8)

Causes of nystagmus of peripheral origin include:

• Vestibular neuritis (usually postinfectious)

• Benign paroxysmal positional vertigo

• Ménière’s disease

Direction-Changing Nystagmus Versus Nystagmus With the Fast Phase in the Same Direction in All Directions of Gaze

Direction-changing nystagmus due to central lesions—Eye movements are generated by a neural pulse that sends the eyes to a target and then a step of continued neural impulses maintaining them there. With central (brainstem/cerebellar) etiologies of nystagmus, there is a problem with the step causing difficulty maintaining gaze. Imagine the consequences of a lesion affecting the step: When the eyes look to the left, there is difficulty maintaining left-gaze, so the eyes drift away from the direction of gaze (slow phase to the right) and are sent back quickly in the direction of gaze (fast phase to the left) to try to maintain fixation—drift away (slow phase to the right)—sent back (fast phase to the left), and so on. The same thing would happen when looking to the right: In attempting to maintain rightward gaze with a lesion affecting the step, the eyes would drift away (slow phase to the left) and be sent back quickly (fast phase to the right). So with a central lesion (affecting the step that maintains gaze), there would be nystagmus with the fast phase in the direction of gaze—left when looking left, right when looking right. Since the direction of the fast phase of the nystagmus changes depending on the direction of gaze, this is called direction-changing nystagmus or gaze-holding nystagmus, and is characteristic of a central cause of nystagmus.

In normal healthy patients, a few beats of nystagmus with the fast phase in the direction of gaze may be seen at the extremes of gaze when testing extraocular movements. This is called end-gaze nystagmus and is generally a benign finding if symmetric and not sustained.

Nystagmus with the fast phase in the same direction in all directions of gaze due to peripheral lesions—When peripheral lesions cause nystagmus, the problem is usually unilateral: either the left or right vestibular apparatus or CN 8 is not working normally. Recall that head turning to either side causes increased CN 8 activity on the side to which the head is turned compared to the other side, leading to movement of the eyes in the direction opposite the direction of head turning (see “The Vestibulo-ocular Reflex” earlier).

Imagine what would happen if there is unilateral peripheral vestibular dysfunction (inner ear or CN 8). Consider the case of a left vestibular lesion (e.g., vestibular neuritis). If there is a lesion affecting the left vestibular apparatus or CN 8, activity in the left CN 8 will be decreased. This leads to an imbalance such that there is relatively more activity in the right CN 8 than in the malfunctioning left side. The brain perceives the greater degree of activity on the right (normal) side compared to the left (malfunctioning side) as the same pattern as when the head is turned toward the right side (right-sided CN 8 activity > left-sided activity), and so this sends the eyes to the left. (The lesion has the same effect as cold water in cold caloric testing; see “Cold Caloric Testing.”) When the patient is not trying to look left, the brain tries to correct the eye movements by sending them briskly back to the right. The eyes drift to the left (slow phase), flick back to the right (fast phase), drift to the left, flick back to the right. No matter what position the eyes are in, they drift to the left, flick back to the right. The fast phase of the nystagmus is therefore always in the same direction no matter what position of gaze the eyes are in: slow phase toward the abnormal side, fast phase away from the abnormal side.

Continuing with the example of a left vestibular lesion, if the eyes do look all the way to the left, this is where the lesion is causing the brain to “want” them to be, so the nystagmus may diminish and even disappear. But when the eyes look furthest away from the lesion—to the right in this example—they are furthest from where the brain “wants” them to be, and so the nystagmus is intensified. This is called Alexander’s law: Peripheral vestibular lesions cause nystagmus that is most pronounced when looking away from the side of the lesion (which is looking in the direction of the fast phase).

Dizziness can be caused by a problem in the nervous system or due to systemic causes. Within the nervous system, the problem can arise from the structures of the inner ear, the vestibulocochlear nerve, the brainstem, or the cerebellum. The inner ear and CN 8 are the peripheral components of this system, and the brainstem and cerebellum are the central components. Localizing the etiology of dizziness requires first determining whether the problem is neurologic or not, since dizziness can be caused by cardiovascular disease (e.g., arrhythmia, orthostatic hypotension), anemia, and endocrine dysfunction (e.g., hypoglycemia, thyroid disease) in addition to neurologic disorders. If dizziness is neurologic in etiology, one must determine whether the problem is peripheral (inner ear or CN 8) or central (brainstem/cerebellum). Medications can also cause dizziness through effects on the nervous system (e.g., antiepileptics), the inner ear (e.g., aminoglycoside toxicity), or the cardiovascular system (e.g., antihypertensives causing orthostatic hypotension).

The classic teaching is that the history in a dizzy patient should aid in classifying the symptom of dizziness as one of the following four entities:

1. Vertigo: a sensation of movement (spinning or tilting)—generally associated with a neurologic etiology

2. Light-headedness/presyncope: generally associated with a cardiovascular etiology

3. Dysequilibrium/imbalance: generally associated with a gait disorder (which may be neurologic or orthopedic, for example)

4. Other/nonspecific: generally associated with a psychogenic etiology

Although it is certainly important to elicit patients’ descriptions of their symptoms, research suggests that patients are inconsistent and imprecise in their descriptions of whether their dizziness is true room-spinning vertigo or not (Newman-Toker et al., 2007), and that patient descriptions do not necessarily correlate well with underlying etiology. An approach centered around timing, triggers, and associated symptoms correlates more closely with pathophysiologic etiology, and these elements of the history are more consistently and accurately reported by patients (Newman-Toker, 2007; Newman-Toker et al., 2007). Within this framework, dizziness is classified as acute or chronic, and chronic dizziness is classified as continuous or episodic. Episodic dizziness is then categorized based on whether the episodes are triggered or spontaneous (Fig. 12–4). If episodes are triggered, the trigger(s) must be elucidated (discussed further below).

Evaluation of Acute-Onset Continuous Vertigo

Acute-onset continuous vertigo is referred to as the acute vestibular syndrome. The differential diagnosis is essentially between posterior circulation stroke and vestibular neuritis (a presumed viral or postviral inflammation of the vestibular portion of CN 8). This is a paradigmatic example of a scenario in which peripheral and central etiologies of vertigo must be distinguished to determine whether dizziness is caused by a benign self-limited condition (vestibular neuritis) or a life-threatening condition (posterior circulation infarct). When obvious localizing findings are present (e.g., ataxia, eye movement abnormalities), the diagnosis of a central nervous system etiology is generally clear. However, many patients present with isolated vertigo, nausea, vomiting, and/or gait unsteadiness without obvious localizing findings on general neurologic examination. Moreover, MRI may be normal in the acute setting of posterior circulation infarction, so a normal MRI is not as reassuring as one would hope in an acutely vertiginous patient.

Fortunately, research has shown that a battery of three bedside tests is highly sensitive and specific for predicting posterior circulation stroke as the cause of acute continuous vertigo: the head impulse test, evaluation of the pattern of nystagmus, and the cover-uncover test for vertical skew deviation of the eyes (Kattah et al., 2009). This battery of tests was given the mnemonic HINTS (head impulse—nystagmus—test of skew) by the authors of the study. A concerning finding on any of these three tests (see below) should raise the index of suspicion for posterior circulation stroke as the cause of acute vertigo and warrants MRI, with repeat MRI after 24–48 hours if initial MRI is normal.

Head Impulse Test

The head impulse test is a test of vestibular function. The examiner asks the patient to fixate on the examiner’s nose and maintain fixation while the examiner moves the head briskly to one side and then the other. Normally, the vestibulo-ocular reflex keeps the eyes fixated on the examiner’s nose, so when the head is moved to the right, the eyes instantly conjugately go to the left to maintain fixation; when the head is moved to the left, the eyes instantly conjugately go to the right to maintain fixation. If there is unilateral peripheral dysfunction (e.g., vestibular neuritis), when the head is turned to the abnormal side, the signal that the head has been turned cannot be transmitted to the central nervous system. As a result, the VOR fails and the eyes go with the head, requiring a catch-up saccade to come back to the nose.

For example, with left peripheral vestibular dysfunction, when the head is turned briskly by the examiner to the right (normal side), the eyes move appropriately instantly back to the left (normal response). When the head is moved briskly by the examiner to the left (abnormal side) there is no VOR, so the eyes also go to the left with the head and then make a catch-up saccade to the right back to the target. A catch-up saccade on the head impulse test to one side only is suggestive of peripheral vestibular dysfunction (inner ear or CN 8). In the setting of the acute vestibular syndrome, a normal head impulse test on both sides has been found to be predictive of stroke as the etiology. Note: the normal finding on this test is the concerning one in this context (i.e., concerning for stroke) since an abnormal head impulse test suggests a peripheral etiology in a patient with acute continuous vertigo.

Direction-Changing Nystagmus

With respect to nystagmus, the pattern concerning for a central etiology of the acute vestibular syndrome is direction-changing nystagmus. Direction-changing nystagmus refers to nystagmus in which the fast phase changes direction with changes in gaze direction: left-beating in left gaze and right-beating in right gaze. This suggests a problem with the gaze-holding mechanism, consistent with a central lesion (see “Direction-Changing Nystagmus Versus Nystagmus With the Fast Phase in the Same Direction in All Directions of Gaze” above).

Test of Skew

Skew deviation is discussed in Chapter 11. Although it can occur with peripheral lesions, it is more commonly seen with central lesions. When vertical skew deviation of the eyes is evident in the acutely dizzy patient, a central etiology should be considered. When subtle, it may not be apparent, but can be elicited by the cover-uncover test. In this test, the examiner asks the patient to fixate on the examiner’s nose, and then the examiner moves one hand back and forth between the two eyes, looking for any vertical readjustment of each eye as it is uncovered. If vertical shifts of the eyes are seen with this test, this is considered a concerning finding for posterior circulation infarct as the cause of acute continuous vertigo.

A mnemonic for remembering the concerning findings in HINTS testing is provided in the study in which it is described: INFARCT: impulse normal, fast-phase (of nystagmus) alternating, refixation on cover-uncover test (Kattah et al., 2009). The presence of any of these three findings in a patient with the acute vestibular syndrome is highly predictive of stroke as the etiology.

It should be noted that this interpretation of this three-test battery is not the same in patients who are not acutely dizzy at the time of examination. Patients often present following an episode of dizziness when they are no longer dizzy. A normal head impulse test will be a normal finding in normal patients, and some patients may have a few beats of end-gaze nystagmus (which is direction-changing). Therefore, while the individual tests of the HINTS battery certainly have important utility in other contexts, the concerning findings in this battery suggest stroke only in a patient with acute-onset continuous vertigo.

Vertigo Accompanied by Acute Unilateral Hearing Loss

The presence of concurrent acute-onset vertigo and acute-onset unilateral hearing loss suggests a problem in the periphery (inner ear or CN 8) since hearing is represented bilaterally quite early in the brainstem auditory pathways and so is not easily disrupted by central lesions. Although most causes of peripheral vestibular lesions are benign, acute-onset unilateral hearing loss is a concerning finding: The inner ear can be infarcted by involvement of the internal auditory artery (also called the labyrinthine artery), which most commonly arises from the AICA. When the finding of acute hearing loss is added to HINTS (“HINTS plus”), the sensitivity for diagnosis of stroke as a cause of acute vertigo (and hearing loss) increases with slight decrease in specificity (Newman-Toker et al., 2013).

Vestibular Neuritis

Vestibular neuritis is diagnosed on clinical grounds when there is acute-onset vertigo following a viral illness and examination findings are consistent with a unilateral peripheral etiology (nystagmus with fast phase in the same direction irrespective of the direction of gaze, abnormal head impulse test). Vestibular neuritis may be treated with a short course of steroids, although data about their efficacy in vestibular neuritis are limited. If symptoms are severe and persistent, a vestibular suppressant (e.g., meclizine) may be considered, but it should be emphasized to the patient that only a short course should be utilized since prolonged use may impair central compensation for peripheral dysfunction.

Hearing loss should not be present in pure vestibular neuritis. If hearing loss is present, the diagnosis of labyrinthitis should be considered. Labyrinthitis may also be postviral, but can be bacterial (e.g., due to meningitis or otitis media). Bacterial labyrinthitis requires antibiotic treatment.

Evaluation of Chronic Dizziness

For patients in whom dizziness is not acute and sustained, the goal of the history is to determine whether dizziness is episodic or continuous, and if episodic, if episodes of dizziness are provoked or unprovoked/spontaneous.

Continuous chronic dizziness can be due to:

• Anemia

• Posterior fossa lesion (for example, tumor, Chiari malformation)

• Medications (for example, antiepileptic, psychiatric, and cardiac medications)

In a patient who presents with episodic dizziness, one must first assess whether episodes of dizziness are unprovoked (i.e., spontaneous) or provoked. Spontaneous episodic dizziness may occur with:

• Cardiac arrhythmia

• Ménière’s disease

• Vestibular migraine

• Posterior circulation transient ischemic attack (TIA)

When dizziness is provoked, specific triggers suggest particular underlying etiologies. Important triggers of episodic dizziness include:

• Moving from supine to seated or seated to standing (suggesting orthostatic hypotension)

• Changes in head position (suggesting benign paroxysmal positional vertigo; see below)

• Exertion (suggesting cardiac etiology)

• Sneezing/coughing/loud noises (suggesting perilymphatic fistula or superior canal dehiscence; see below)

Another feature of the clinical history that can be helpful is the length of episodes of vertigo:

• Seconds to minutes: benign paroxysmal positional vertigo (See “Benign paroxysmal positional vertigo” below)

• Minutes to hours: Ménière’s disease, transient ischemic attack (TIA), migraine

Episodic Dizziness Provoked by Positional Changes: Orthostasis and Benign Paroxysmal Positional Vertigo

Any patient who is already dizzy will likely feel that dizziness worsens with head position, as anyone who has been “sea sick” can confirm. The question here is whether the onset of dizziness is provoked by position change. Dizziness provoked by changes in body position (supine to seated or seated to standing) suggests orthostasis, and orthostatic vital signs should be obtained. Dizziness provoked by changes in head position (e.g., rolling over in bed) suggests benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo—Benign paroxysmal positional vertigo (BPPV) is caused by irritation of a particular semicircular canal by an otolith. The most commonly affected semicircular canal is the posterior canal, although anterior and horizontal canal BPPV occur rarely. BPPV is diagnosed by the Dix-Hallpike test in which the patient looks over one shoulder in the seated position and is then rapidly placed in the supine position with the head supported in the examiner’s hands and tilted below the level of the examining table while still turned to the side. The test is repeated on each side. In classic BPPV of the posterior semicircular canal, when the head is turned toward the affected side, after a delay of several seconds, the patient will experience vertigo and a mixed upbeat rotatory nystagmus will emerge with the rotatory fast phase toward the ground and the up-beating component more prominent in the upper eye (Fig. 12–5).

If the Dix-Hallpike maneuver elicits downbeat nystagmus that appears without delay, a central etiology should be considered and neuroimaging should be obtained.

Posterior semicircular canal BPPV can be treated at the bedside through the Epley maneuver (Fig. 12–6). This begins like the Dix-Hallpike maneuver (head back and turned toward the affected side; Fig. 12–6A). After 1 minute, the patient’s head is turned 90 degrees (now facing away from the affected side and still tilted below the level of the examining table; Fig. 12–6B) for 1 minute. Then the patient turns the body toward the head to lie on the side, which puts the head in the downward-facing position (Fig. 12–6C). After 1 minute, the patient returns to the seated position (now 90 degrees from the original seated position; Fig. 12–6D). It is common for the patient to feel a recurrence of vertigo when returning to the seated position, and nystagmus may reemerge in the direction opposite the direction observed during the Dix-Hallpike maneuver. If the symptoms are convincingly reproduced on one side only by the Dix-Hallpike maneuver but no nystagmus is observed, it is still reasonable to perform the Epley maneuver on that side since nystagmus may be quite subtle.

Anterior and horizontal canal BPPV are rare, and generally occur only as complications of the Epley maneuver for posterior canal BPPV such that the otolith that was originally in the posterior canal ends up in one of the other canals.

Anterior canal BPPV causes downbeat torsional nystagmus rotating toward the ceiling (away from the downward-facing ear) on Dix-Hallpike testing. However, as noted above, since downbeat nystagmus can be an indication of a central etiology of vertigo, and given the rarity of anterior canal BPPV, neuroimaging should be obtained if downbeat nystagmus is elicited. Since anterior canal BPPV is a rare condition, appropriate canal repositioning maneuvers for anterior canal BPPV are not well established.

Horizontal canal BPPV requires a different maneuver to be diagnosed: The patient is placed in the supine position and the head is rapidly rotated to one side and then the other, looking for pure horizontal nystagmus, which may be toward the ground (geotropic) or toward the ceiling (ageotropic), and may change position with the head on either side. The affected side is generally considered the side toward which the nystagmus appears more prominent when the nystagmus is geotropic, and the side to which it is less prominent with ageotropic nystagmus. Repositioning maneuvers to treat horizontal canal BPPV include the 360 roll maneuver (also called the Lempert maneuver) and the Gufoni maneuver.

In the Lempert (360 roll) maneuver, the patient begins in the supine position with the head turned such that the affected ear is down, then begins a series of 90-degree turns of the head—to looking at the ceiling, to looking to the side opposite the original side, to lying prone and looking down, to laying on the side of the affected ear (affected ear down), to supine, to seated (360 degrees). In the Gufoni maneuver, the patient goes from the seated position to laying on the unaffected side, then looking down (head turned over shoulder) while in that position, followed by returning to the seated position with the head still turned over the shoulder.

Episodic Dizziness Provoked by Loud Noises (Tulio’s Phenomenon) or Coughing/Sneezing: Perilymphatic Fistula and Superior Semicircular Canal Dehiscence

The symptom of dizziness triggered by loud noises (called the Tulio phenomenon), coughing, and/or sneezing is suggestive of two rare conditions of the inner ear: perilymphatic fistula and superior semicircular canal dehiscence. Perilymphatic fistula is a fistula between the middle ear and the inner ear, usually secondary to trauma. In superior semicircular canal dehiscence there is thinning of the temporal bone superior to the superior semicircular canal. In addition to the symptoms listed above, semicircular canal dehiscence can cause the symptom of autophony: patients report hearing their own heartbeat, chewing, and other internal sounds. Both conditions require imaging of the temporal bone and consultation with an otolaryngologist since surgical intervention may be indicated.

Unprovoked Episodic Dizziness

Ménière’s disease—Ménière’s disease is caused by idiopathic development of increased pressure in the inner ear (endolymphatic hydrops). The condition usually develops between early adulthood and late middle age (20s–50s). Episodes last hours and include vertigo, hearing loss, tinnitus, and a sensation of ear fullness. There may be progressive hearing loss and/or tinnitus between attacks. Patients may report sudden falls without loss of consciousness or vertigo, called otolithic crises of Tumarkin. The diagnosis is clinical, but audiometry may reveal fluctuations over time and/or progressive low-frequency hearing loss. Initial treatment includes low-salt diet and a diuretic. In refractory cases, labyrinthectomy or intratympanic gentamicin administration may be performed to ablate the inner ear.

Cogan’s syndrome causes Ménière-like attacks and interstitial keratitis. The syndrome can be seen in association with systemic vasculitis, or may occur in isolation.

Vestibular migraine—Dizziness is common in migraine, but some patients have severe vertigo as the prominent feature of their migraines (vestibular migraine). Nystagmus of any type may be observed during or between episodes in patients with vestibular migraine. Some patients may have episodic vertigo without accompanying headache, in which case the diagnosis of vestibular migraine is one of exclusion when no alternative explanation can be found after appropriate evaluation. Acute and preventive treatment of vestibular migraine is the same as for migraine in general (see “Treatment of Migraine” in Ch. 26), although meclizine, an antiemetic, or a benzodiazepine may be added to the acute abortive regimen for treatment of vertigo during acute migraines.

Posterior circulation transient ischemic attack (TIA)—Posterior circulation TIA should be considered in patients with episodic vertigo with vascular risk factors or history concerning for vertebral artery dissection (e.g., recent trauma) (see “Transient Ischemic Attack” in Ch. 19). In patients with recurrent episodes of vertigo concerning for posterior circulation TIAs, vascular imaging of the head and neck should be obtained to evaluate the vertebrobasilar system.

An important and life-threatening nonneurologic etiology of unprovoked episodic dizziness to consider is cardiac arrhythmia.